Pharmacology Flashcards
define pharmacodynamics
what a drug does to the body
define pharmacokinetics
what the body does to a drug
define a drug
any single synthetic or natural substance of known structure used in treatment, prevention or diagnosis of a disease
define a medicine
chemical preparation containing one, or more, drugs used with the intention of causing a therapeutic effect.
examples of regulatory proteins that drugs act on?
enzymes, carrier molecules (transporters and pumps), ion channels and receptors
define an agonist
a drug that binds to a receptor to produce a cellular response e.g. adrenaline
define an antagonist
a drug that reduces or blocks the actions of an agonist by binding to the same receptors e.g. beta blockers
define affinity of an agonist
strength and association between a ligand and receptor
define efficacy of an agonist
ability of an agonist to evoke a cellular response
do antagonists possess affinity and efficacy?
only affinity
define EC50
the concentration of an agonist that elicits a half maximal response
same EC50
equipotent
what type of competition occurs between agonists and antagonists?
competitive inhibition if they bind to the same site, but different site is non-competitive
non-competitive inhibition causes the curve to?
not reach max
competitive inhibition causes the curve to
shift to the right
receptors are targets of?
neurotransmitters,hormones, therapeutic agents
three different ways of chemical signalling
- autocrine
- paracrine
- endocrine
four main types of receptors
- ligand-gated ion channel
- G protein-coupled receptor
- kinase-linked receptor
- nuclear receptors
structure of a ligand-gated ion channel
separate glycoprotein subunits with binding sites
which receptors are involved in second messengers?
G protein-coupled receptors
structure of G protein-coupled receptors
integral membrane protein. single polypeptide with NH2 and COOH, 7 transmembrane alpha-helical spans joined by 3 intracellular and 3 extracellular loops
structure of G-protein
peripheral membrane protein with 3 polypeptide subunits (alpha, beta and gamma). Guanine binding site on the alpha subunit that holds GTP or GDP
how is the G protein coupled receptor activated?
binding of the agonist
how is the G protein activated
the activation of the G-protein coupled receptor causes conformational change in the alpha subunit of the G-protein
what three changes happen to the G-protein to make it activated?
- G-protein couples with receptor
- releases GDP and GTP binds
- subunit dissociation
how do you turn off the signal even when the agonist has dissociated?
alpha subunit acts as an enzyme hydrolysing GTP to GDP. Subunit recombination.
explain signalling via receptor kinases
binding causes autophosphorylation and recruitment of proteins
explain nuclear receptors
steroid hormones diffuse across the plasma membrane and combine with an intracellular receptor which moves to the nucleus which switches genes on or off
four fates of drugs in the body
- Absorption
- Distribution
- metabolism
- excretion
what is metabolism and excretion collectively called?
elimination
four factors that affect drug absorption
- solubility
- chemical stability (destroyed by acid, etc.)
- lipid to water partition coefficient (ability to diffuse across the membrane)
- degree of ionisation
define pKa
pH when 50% of the drug is ionised
where are weak acids absorbed
stomach lumen, but also small intestine
where are bases absorbed
small intestine
do acidic drugs become less ionised in acid environments
yes
factors affecting GI absorption are?
- GI motility (rate of stomach emptying)
- pH at absorption site
- blood flow
- way the tablet is manufactured (capsule)
- presence of transporters
advantages of oral administration
simple, convenient, non-sterile
disadvantages of oral administration
inactivation by enzymes and acid, variable absorption
define oral availability
fraction of drug that reaches systemic circulation after oral ingestion
define systemic circulation
fraction of drug that reaches systemic circulation after absorption
advantages of sublingual administration
rapid absorption
disadvantages of sublingual route
infrequent, few preparations available
advantages of rectal administration
useful when oral route compromised
disadvantages of rectal administration
infrequent, variable absorption
advantages intravenous
rapid onset
disadvantages of intravenous
sterile preparation required, risk of sepsis
advantages of intramuscular
rapid onset
disadvantages of intramuscular
painful
which free drugs can move between compartments in the body?
ionised and unionised drugs that are not bound to plasma proteins
volume of distribution equation
dose / plasma concentration
define drug clearance
the volume of plasma cleared of drug per unit of time
clearance determines the?
dose rate
define chemical equivalence
the drug product contains the same amount of active compound
define volume of distribution
the volume into which a drug appears to be distributed with a concentration equal to that of plasma
what is different about a loading dose?
it is an initial higher dose before dropping down.
define xenobiotics
foreign chemicals
five things drug metabolism can do
- convert parent drug to a more polar form
- convert it to a less pharmacologically active form
- convert inactive to an active form
- unchanged activity
- change spectrum of action
describe phase 1 of drug metabolism
makes drugs more polar, adds a chemically reactive group, permits conjugation. Serve as a point of attack for phase 2
describe phase 2 of drug metabolism
adds an endogenous compound increasing polarity
where do phase 1 reactions take place
liver
what proteins carry out phase 1
CYP450
what are CYP450’s
ahem proteins located on the ER of liver hepatocytes
describe the three stages of the P450 cycle
- drugs enter the cycle
- O2 provides two atoms of oxygen
- one oxygen forms water and the other oxygen forms a hydroxyl product
what does phase 2 usually result in?
inactive products
define glucuronidation
transfer of glucuronic acid
three processes carried out by the kidneys in drug excretion
- glomerular filtration
- active tubular secretion
- passive reabsorption by diffusion
what happens in glomerular filtration?
many drugs bind reversibly to large plasma proteins. Only unbound drugs can enter the filtrate.
what are the two transporter systems that secrete drugs into the lumen of the nephron?
- organic anion transporter
2. organic cation transporter
describe the organic anion transporter
organic anions enter the cell by diffusion or in exchange for alpha-KG. At the apical membrane OA- enters
describe the organic cation transporter
organic cations enter by diffusion and enter via the apical membrane
factors influencing tubular reabsorption are
- lipid solubility
- polarity
- urinary flow rate
- urinary pH
what is Ke
elimination rate
define elimination rate
amount of drug eliminated per unit of time